The invention concerns a shutter, particularly a louver type shutter, for ventilation systems having at least one hollow flap which is pivotally mounted in a frame and further having a seal between the flap and the frame which is made from a foam sheet covered on the surface facing the frame with a thin coating of a material having a fairly good sliding capability.
A shutter of this type is known from German Utility Model No. 77 33 240. The Utility Model suggests in particular a number of variants of a seal which, like those in accordance with German Utility Model Nos. 76 28 312 and 77 33 239, is fitted on the outside of a toothed wheel seated on and capable of moving the flap and, in the case of a folding cover, coupling the flap with a neighboring flap.
A basic problem with these seals, also dealt with in the first-mentioned Utility Model, is in the contact pressure. Since all manufacturing defects, especially the unavoidable slight distortions of the metal frame, are absorbed by the foam sheet or seal, the average compression of the seal, and thus the contact pressure is sometimes excessible. The flap is then too slow-moving. This impairs its efficiency, particularly in the event of a power failure when it is supposed to close automatically by means of prestressed spiral springs which do not have the power of an electrical motor.